This invention relates generally to torsional couplers, and more particularly to helical wrap spring torsional couplers used in transferring rotation motion and torque from a rotational driving member to a rotational driven member. For example, a torsional coupler used for transferring torque from a shaft to a pulley.
Conventional methods of torionally coupling a machine element to a shaft are set-screws, keys, cotter pins, split collars with cross methods suffer from slow installation and removal, unpredictable and low torque transfer from the shaft to machine element and difficult or slow axial location adjuastment.
Prior art wrap spring torsional couplers are used for transferring or limiting torque, within clutches, brakes and specialty apparatus. A wrap spring transfers unidirectional torque from a conical shaped shaft to a driven pulley in Ludlam, U.S. Pat. No. 1,166,379, with the object of providing torsional resiliency and direct torque release when reversing the rotational direction of the driving member. Prior art using a single wrap spring to transfer torque include the clutches described in McGibbon, U.S. Pat. No. 1,523,772, Mehrbrodt, U.S. Pat. No. 3,905,458 and Janning, U.S. Pat. No. 3,934,690. Although different from a direct torque coupler, where the gripping action of the wrap spring transfers total torque, Takada, U.S. Pat. No. 5,620,372, Kaplan, U.S. Pat. No. 3,242,696 and Weninger, U.S. Pat. No. 4,090,785, show dual diameter wrap spring torque limiters, utilizing the unwrapping of a wrap spring resulting in controlled or constant friction slip between the wrap spring and driven member. Corrigan, U.S. Pat. No. 5,947,409, describes dual diameter wrap springs used to transfer torque while providing radial compliance for web tension control. Prior art does not describe a bi-directional torsional coupler, such as the invention, having means for releasing the wrap spring gripping action during coupling installation and coupling axial adjustment on a common cylindrical drive shaft of any length.
One object of the present invention, here after called "bi-directional torsional coupler" or "coupler", is to provide bi-directional torque transfer between a shaft and the bi-directional coupler's integral mechanical element such as a pulley, sprocket, gear or cam. The bi-directional torsional coupler contains two wrap spring coils, each wound in a direction of opposing gripping actions, thereby providing bi-directional torque transmission between a shaft and the mechanical element part (pulley, gear, sprocket or cam) of the bi-directional torsional coupler. Conventional prior art torsional power transmission couplers are uni-directional.
Another object of the present invention is to provide a means for releasing the gripping action of each of the wrap springs of the bi-directional torsional coupler, thereby allowing quick assembly to a shaft or quick dis-assembly from a shaft. A manually rotatable end cap on each end of the invention, engages each wrap spring end tang, whereby manual rotation of an end cap unwinds, and enlarges the wrap spring coil diameter, releasing the gripping action to the shaft. The releasing of gripping to the shaft also allows quick and easy axial adjustment of the bi-directional torsional coupling on a shaft. Conventional prior art wrap spring torsional power transmission couplers are not quickly assembled, are not quickly dis-assembled, and do not allow quick axial adjustment from a shaft, after installation.
The present invention is a bi-directional, dual wrap spring torsional coupler with means to decouple and relieve the gripping action to a shaft. A machine element, integral to the invention, such as a pulley, sprocket, gear or cam, is a mechanical driven member, and serves as a means for external power transfer.
The single embodiment of the bi-directional torsional coupler invention uses two conventional wrap springs (Ludlam, U.S. Pat. No. 1,166,379) having a smaller diameter, inner helical spring portion connected to and surrounded by a larger diameter outer helical spring portion; the transition between the inner and outer spring portions being of a spiral shape (Ludlam, U.S. Pat. No. 1,166,379). The two wrap springs are wound in a direction of opposing gripping actions, thereby providing bi-directional torsional transfer to a shaft. The wrap springs transmit the torque from a shaft to the an outer diameter of the bi-directional torsional coupler's machine element (pulley, gear, cam) for one direction of torque transmission and to the outer diameter of the bi-directional torsional coupling's hub for the opposite direction of torque transmission. The bi-directional torsional coupler's machine element member is rigidly attached to the coupler's hub after the manufacturing assembly of both wrap springs. The smaller diameter, inner spring coil portion of each wrap spring, wraps around, and grips a drive shaft; the larger diameter spring coil portion of each wrap spring, wraps around and grips outer diameter portions of the invention's machine element (pulley, gear, cam) or the attached hub. The spiral spring wire transition between the inner and outer wrap spring coils, as in other conventional wrap springs (Ludlam, U.S. Pat. No. 1,166,379), is supported by a spiral shaped groove (Ludlum, U.S. Pat. No. 1,166,379), to better insure tensile type wire stress and minimize wire bending stresses. The bi-directional torsional coupler invention provides means for unwrapping, and releasing the grip of each wrap spring to the shaft, wherein the coupler's rotatable end caps engage each end wrap spring inner coil tang that extend outward in an axial direction. One end cap is assembled, with rotational freedom, to the bi-directional torsional coupler's machine element (pulley, gear, cam) driven member with end cap engagement of one wrap spring end tang, and the other end cap is assembled, with rotational freedom, to the bi-directional torsional coupler's hub with the end cap engagement of the other wrap spring end tang.